PSI - Issue 25

L. Martelli et al. / Procedia Structural Integrity 25 (2020) 294–304 Lucrezia Martelli/ Structural Integrity Procedia 00 (2019) 000–000

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Columns cross-sections change depending on their position:  HEB300 section bars are used at east-west ends of the main façades, on either side of the entrance staircase and all around the new stairwell/elevator shaft;  HEA200 structural steels have been introduced in any other case. Taking about beams, they are arranged as follows:  HEA180 bars belong to the frame;  HEA100 sections for connections between the existing structure and the external one; they are placed at each floor like rigid links.

Fig. 3. FE model of the existing structure

Dealing now with cross-shaped bracings, three different solid section rods appear:  Φ120 types have been introduced on x-z plane like reinforced elements for stairwells, to cover the spans between HEB300 pillars of north and south facades, on y-z plane along the short sides of the building and sometimes on the north façade as a way to stiffen along y-direction where needed;  Φ50 bars have been placed on vertical x-z and y-z planes to transfer seismic actions at nodes from the existing floors to the exoskeleton aiming at avoiding the onset of bending moments; they are also on horizontal x-y plane. Each node of the exoskeleton has been located outside of the existing floors no matter was the level, in order to let the two structures work separately towards the same goal. Exoskeleton pillars have fixed supports at the base, corresponding to 2.30 m, i.e. the level fromwhich primary building raises. Moreover, in the interests of safety, analysis have been executed setting up a minimum vulnerability index equal to � � ���� , as to assure the highest level of adjustment Italian Standard NTC (2018) grants. The final axonometric view of the retrofitted system emerges in Figure 4. It can be noticed that the introduction of the exoskeleton has enabled to make a more regular floor plan (Figure 5), unlike it was before. In fact, despite observing distance limitations between adjacent buildings as reported in Interdepartmental Ordinance no.1444 (1968), a rectangular perimeter has been created wherever possible.